Combustion engines may generate harmful emissions. For example, diesel engines are known to emit carbon monoxide (CO), nitrogen oxides (NOx), unburned hydrocarbons (HC), and particulate matter (PM). Catalysts may be provided on various surfaces in the exhaust flow path of a vehicle in an attempt to reduce, or eliminate these emissions. These catalysts may help facilitate reactions that take place in the exhaust flow in order to ensure that the gases that are eventually emitted from the vehicle fulfil the increasingly stringent emission legislation and/or carbon dioxide fleet average targets or emission and carbon dioxide city or market incentive targets.
In order to optimise catalysed reactions within the exhaust pathway, the inlet and outlet cones may be designed to encourage uniform gas flow across the catalyst. In addition, flow obstructions may be provided within the exhaust pathway to try to improve the flow characteristics of the exhaust gases. However, such design constraints on the inlet and outlet cones and the obstructions all have implications on the packaging requirements of the exhaust system. These packaging requirements may conflict with other engine and/or vehicle design targets. For example they may compete with increasingly separate vehicle structural integrity and passenger safety measures, in particular in the event of a crash.
In applications where catalyst is applied homogeneously across a surface, a front face or area of the catalyst surface may degrade more rapidly than other parts of the catalyst surface. Therefore, in order to meet in-use compliance there has been a need to add to the catalyst volume. However, this may be at the expense of packaging requirements, as the overall system volume may be increased. Zone wash-coating on the substrate surface has therefore been used for catalyst washcoating. Traditional zone coating encompasses the provision of an increased concentration of catalyst on the first part of the surface which the exhaust gases are incident on, during use. This zone coating acknowledges that the front part of the surface may degrade more quickly as it may be the first part of the surface on which the exhaust gases are incident. The exhaust gases may contain the highest level of contaminants and the highest temperatures as they impact this part of the catalyst surface. The loading of the catalyst to the front of the catalyst surface may also enable the exploitation of heat flux efficiencies during catalyst light off as well as enabling catalyst volume reduction and/or catalyst material optimisation (reduce use of high value catalyst content).
Traditional zone coating may effectively increase the lifespan of catalyst surfaces by providing an increased catalyst concentration in the front part of the surface. Traditional zone coating assumes that the flow of the exhaust gases is substantially homogenous. However, inventors herein have recognized that failure modes in catalyst surfaces within exhaust systems tend to show that the flow of exhaust gases may be non-homogenous and largely attributable, but may not be exclusively attributable to the aforementioned constraints, for example attributable to additional exhaust systems bends resulting from added hardware and packaging constraints. Non-homogeneous flows may also result from some optimisations of engine design.
U.S. Pat. No. 9,333,490 to Kazi et al. discloses a zoned catalyst for diesel applications. An oxidation catalyst composite is disclosed wherein two washcoat zones differ by particular Pt/Pd ratios, and particular length ratios. However, the inventors herein have recognized shortcomings with this approach. For example, the relative locations of the zones differ only in that the first zone is upstream from the second zone, and the zoned surface is oriented only longitudinally with the exhaust flow direction.
According to the present disclosure there is provided a method of applying a non-homogenous catalyst coating to a surface, the method may include: partially masking the surface with a first template; applying a first washcoat slurry to those parts of the surface not masked by the first template; partially masking the surface with a second template; and applying a second washcoat slurry to those parts of the surface not masked by the second template. In this way, the surface may have a catalyst material that differs along a direction transverse to the exhaust flow direction, and may differ in both a longitudinal and transverse direction. Also in this way, the catalyst material may be varied on the surface in particular ways that may be better suited for non-homogeneous flow.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.